NullPointerException beim Sortieren benutzerdefinierter Objektliste

Question

Ich möchte meine benutzerdefinierte Liste basierend auf Feld sortieren. Meine Liste hat ungefähr 125 Datensätze, da es statisch ist.

Collections.sort(receivedSOSModelArrayList, new Comparator<ReceivedSOSModel>() { 
    @Override 
    public int compare(ReceivedSOSModel receivedSOSModel, ReceivedSOSModel t1) { 
     return receivedSOSModel.getReceivedSOSFrom().compareTo(t1.getReceivedSOSFrom()); 
    } 
}); 

Aber auf oben genannten Code nur nach dem Hinzufügen aller Objekte in der Liste aufrufen. Ich bekomme einen Fehler.

java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.compareTo(java.lang.String)' on a null object reference 
    at com.xx.xx.Activities.sos.SOSReceivedActivity$4.compare(SOSReceivedActivity.java:366) 
    at com.xx.xx.Activities.sos.SOSReceivedActivity$4.compare(SOSReceivedActivity.java:355) 
    at java.util.TimSort.binarySort(TimSort.java:261) 
    at java.util.TimSort.sort(TimSort.java:204) 
    at java.util.Arrays.sort(Arrays.java:1998) 
    at java.util.Collections.sort(Collections.java:1900) 
    at com.xx.xx.Activities.sos.SOSReceivedActivity.compareList(SOSReceivedActivity.java:355) 
    at com.xx.xx.Activities.sos.SOSReceivedActivity.loadDataToRecyclerView(SOSReceivedActivity.java:318) 
    at com.xx.xx.Activities.sos.SOSReceivedActivity.access$100(SOSReceivedActivity.java:44) 
    at com.xx.xx.Activities.sos.SOSReceivedActivity$1.onDataChange(SOSReceivedActivity.java:126) 
    at com.google.android.gms.internal.zzakg.zza(Unknown Source) 
    at com.google.android.gms.internal.zzalg.zzcxk(Unknown Source) 
    at com.google.android.gms.internal.zzalj$1.run(Unknown Source) 
    at android.os.Handler.handleCallback(Handler.java:746) 
    at android.os.Handler.dispatchMessage(Handler.java:95) 
    at android.os.Looper.loop(Looper.java:148) 
    at android.app.ActivityThread.main(ActivityThread.java:5443) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 

Answer 1

null Kontrollen hinzufügen vor dem Vergleich:

Collections.sort(receivedSOSModelArrayList, new Comparator<ReceivedSOSModel>() { 
    @Override 
    public int compare(ReceivedSOSModel receivedSOSModel, ReceivedSOSModel t1) { 
     if (receivedSOSModel == null || receivedSOSModel.getReceivedSOSFrom() == null) { 
      Log.v("first", "NULL"); 
      return -1; //null values will be displayed at bottom in sorted list 
     } 

     if (t1 == null || t1.getReceivedSOSFrom() == null) { 
      Log.v("second", "NULL"); 
      return 1; //null values will be displayed at bottom in sorted list 
     } 

     return receivedSOSModel.getReceivedSOSFrom().compareTo(t1.getReceivedSOSFrom()); 
    } 
});